Means for remote tuning of radio receivers



March 29, 1938. c. PELMULDER ET Al.

MEANS FOR REMOTE TUNING OF RADIO RECEIVERS Filed Deo. 8, 1936 NDL ONK.

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Patented Mar. 29, 1938 UNITED STATES PATENT OFFICE MEANS FOR REMOTE TUNING 0F RADIO RECEIVERS ration of Nevada Application December 8, 1936, Serial No. 114,782

7 Claims.

Our invention relates to a means and method for the supervisory tuning of radio receivers from a transcribing station located at a distance from a radio receiver, and more particularly to a system which employs a single telephone pair simultaneously energized for supervisory tuning and for transmission of the radio signals. It is particularly adapted for use when a transcribing station is located at such a distance from the receiver that the greatest possible economy in the use of connecting wires must be obtained.

Among the objects of our invention are: To utilize a single telephone pair between a transcribing station and a radio receiving station for the simultaneous transmission of the radio signals to the transcribing station and tuning control impulses from the transcribing station; to provide a means and method of controlling the tuning of a remote radio receiver over a standard telephone line; to provide a means and method of controlling the tuning of a remote radio receiver by impulses carried by the same telephone pair that carry the received signals to the transcribing station; to provide a means and method of sending radio signals and tuning control impulses over a single telephone pair wherein only the audio-frequency rights are available; and to provide a means and method of utilizing an existing common power source for the control of a radio receiver situated at a distance from a transcribing station.

Our invention possesses numerous other objects and features of advantage, some of which, together with the foregoing, will be set forth in the following description of specific apparatus embodying and utilizing our novel method. It is therefore to be understood that our method is applicable to other apparatus, and that we do not limit ourselves, in any way, to the apparatus of the present application, as we may adopt various other apparatus embodiments, utilizing the method, within the scope of the appended claims.

The figure is. adiagram showing a preferred circuit for the practice of our invention, the diagram being reduced to lowest terms and being shown without such accessories as switches, fuses, limiting resistors, meters, spark Suppressors, power factor correction condensers, or repeaters which might be required on longer lines.

It often occurs that a radio receiving station is located on the outskirts of a city, or beyond, in order to reduce interference to a minimum and in order to obtain proper directional characteristics of the receiver antenna system. It is often advantageous to transmit the received signals to a downtown location where messages received may be quickly and efliciently dispatched to their addressees` It is also obvious that in such an arrangement the greatest possible economy in the use of connecting wires must be obtained, and, for example, it is common practice to utilize a standard telephone connection between the receiving station and the transcribing station, the signals passing through the telephone switchboard system exactly as do telephone conversations. Under these circumstances the use of a standard telephone pair on which audio frequency rights only are available would be much cheaper than the use of special circuits.

The main difficulty, however, in transcribing signals coming to a transcribing station through a telephone pair from a remote receiver lies in the fact that the radio signals to be received may accidentally or purposefully vary somewhat from time to time in frequency, and if an oscillating radio receiver is utilized the local oscillator will also vary somewhat in frequency.

It is, therefore, of great advantage that the transcribing operator should have a supervisory control of the tuning of the receiver in order that the signal volume be maintained by retuning as oscillator or signal frequencies change. It is also at times desirable to vary the output frequency of an oscillating receiver to avoid interfering signals or to meet the personal differences in the hearing of various operators. Modern receivers and transmitters do not diverge widely from that frequency to which they are adjusted, and it is obvious, therefore, that a large latitude in tuning supervision is not necessary.

Ordinarily, such supervisory tuning would have to be exercised over a separate circuit than that used for the reception of the signals. Such duplication of connections, however, is expensive, and our present invention allows both the tuning supervision impulses and the signal impulses to pass simultaneously, without interference, through the same telephone pair, thus greatly reducing the expense and allowing the operator at the transcribing station to control at all times the tuning of the receiver giving forth the signals to which he is listening.

inasmuch as ordinary telephone pairs are designed to carry audio impulses only, We prefer to utilize, for tuning control power, commercial alternating current which is taken from the same alternating current power system that supplies the receiving station, and since the frequency of this alternating current in the power system is usually 6G cycles per second, and the received signals are usually on the order of 1000 cycles per second, it is obvious that they may be passed over an ordinary telephone pair without interference with central station equipment or change of central station design.

Referring directly to the drawing for a more detailed description, a radio receiver I, having a split symmetrical main tuning condenser 2, balanced with respect to ground, is further provided with a split remote control band spread condenser 2' of relatively smaller capacitance, in parallel with the main tuning condenser, and with a split remote control condenser 3 of relatively larger capacitance, connected in series between the two sections of condenser 2' by lead wires 2, which on account of their proximity to ground potential in the balanced condenser system, may be of relatively great length without affecting the tuning range. The remote control condenser 3 is preferably rotated through the medium of friction discs 4 by a tuning motor 5. 'I'he tuning motor is preferably a synchronous motor with a built-in reduction gear, not shown, but obviously may be any suitable type of motor which can be reversed. 26

'I'he motor 5 is controlled by a contactor assembly which comprises a forward contacter 6, a backward contactor 1, and a running contactor 8, all supplied from A. C. mains Il through contactor leads III and receiving station leads Il. .The forward contactor 6 and backward contactor 1 `are controlled by coils I2 and I4 through contacts I5 and movable arms I6, of a dierential polar relay having coils I1 and I6. Arm I6 is attached to one of the contactor leads I0 through wire It and the return side of contact coils I2 and I4 connected by wire 26 to the other of the A. C. leads I0. 'Ihe common point of relay coils I1 and I6 is connected to the midpoint of an A. C. transformer 2I by a/ relay lead 22, and the ends of relay coils I1 and I6 lead to cathodes 26 and 24 of a pair of double thermionic tubes 21 and 26. While it will be obvious to those skilled in the art that the double cathode tubes herein to be described are the full equivalent of four separate tubes, simpiicityfof wiring makes the double tube more advantageous.

Considering the tube assembly for operating the differential relay, the primary 26 of the transformer 2| is attached to station A. C. leads II and one end of the secondary is connected directly to anode26 of the tube 21 and to anode 20 of tube 26. The other end of the secondary of transformer 2I goes to another anode II in the tube 21 placed on the opposite side of cathode 2l, and

similarly to a second anode 32 in tube 26. Thus the anodes similarly positioned in both tubes are in parallel, and opposite anodes are connected to` opposite ends of the secondary of transformer 2I and will thus be always out of phase in the same Two grids are provided for each tube between the cathode and each anode. In tube 21 grids I3 and 34 are connected to the ends of secondary 25 of grid transformer 3l. Similarly, in tube 26. grids 21 and Il are placed between cathode 24 and anodes 20 and 22, and are connected to the ends "of a second grid transformer 4I. 'Ihe primaries 4I andk 42 of transformers I6 and 4l are connected together in parallel. but in reverse phase. and are supplied with energy from secondary 42' of hybrid coil 43, which is connected to standard telephone line 44 leading to the transcri ing station through the medium of the hybrid coil 43 and balancing impedance 4I, asy iseustomary in the art when energy flowing in opposite directions 1S handle@ on the same pair. Output leads 46 from the receiver I lead to the hybrid coil assembly, one of them being connected directly to the line and the other to an intermediate point in the hybrid coil primary. Simplex channel 48 is not available for use in this service.

When the telephone pair 44 reaches the transcribing station it enters a hybrid coil and balancing impedance network 46 similar in all re spects to the one at the receiving station. Secondary 41 of assembly 46 leads to a pair of receiving telephones 48 or a loud speaker, as the case may be. Alternating current is supplied to the hybrid coil of assembly 46 through control leads 49 attached to the primary of the hybrid coil and directly to the line, and leads 49 emerge from a reversing switch 50 which is supplied by the secondary 5I of a control power transformer 52, the primary 53 of which is attached to the A. C. power lines 9, these being supplied by the same power system that supplies the. receiver.

Having described the circuital arrangement of our invention in its lowest terms, we will now describe the operation:

The receiver I is tuned roughly by hand, b the operator in charge of the receiving station, to the center of the general frequency band from which signals are to be transcribed, and the remote control tuning condenser 3 is rotated so that it is in the midpoint of the tuning range desired. If coarse tuning with a large range is desired, the band 4spread condenser 2 is set to a high capacitance, while if fine tuning with a smaller range is desired, it is set to a low capacitance. Signals thereupon emerge from the receiver I, pass along line 46 to hybrid coil 43, and thence over the telephone pair 44, through the. hybrid coil of assembly 46', and are heard at the transcrlbing station through receiver 46. The operator listens to the signals, and if he finds that he wishes to change the tuning of the receiver he operates reversing switch 60. The circuit diagram gives, by means of'plus and minus signs, the phase conditions that will exist at one particular point in the A. C. cycle, when the arm of the reversing switch is h eld to the left. Y

For example, let us suppose that reversing switch 66 is in the midpoint so that no A. C. energy is passing into the telephone pair. Under these conditions all grids of the two tubes are maintained at a uniform bias by means of bias batteries 6I and 62, and the anode current through both tubes is equal and oppositely directed with respect to the magnetic field in coils I1 and Il, thus balancing the arm I6 of the diiferentiai polar relay midway between contacts Iland the motor does not turn. When, however, it is desired to run the tuning motor. reversing switch 60 may be operated either to the left or right, and a small amount of A. C. power passes into the local hybrid network. Due to the balance of the local hybrid network this power does not reach the local receivers, but a portion of its goes out over the telephone pair to the hybrid network at the receiving station, where balancing network 4l is preventing-the receiver signals from operating the motor.' The A. C. power, however, will CFI aliases coming alternating current, whereas the phase on the anodes will not be changed. Thus it will be Seen that if the reversing switch be held to the left, then tracing through the polarities, the upper right grid is also positive, permitting current flow to the upper filament, while in each of the three remaining combinations of anodes and grids either plate or grid is negative, preventing increase of current flow. One half-cycle later the left upper grid and left upper plate will be positive, so that current will still ow to the upper filament. Thus, as long as the reversing switch is held to the left a pulsating double frequency current is passed through the upper filaments to the upper coil I8 of the differential polar relay, deflecting the arm I6 of the relay upward, thus energizing forward contactor 6 and running contactor 8. If the reversing switch be held to the right the two sides of the lower tube become alternately active, delecting the arm I6 of the relay downward and energizing the backward contactor 1, which supplies current to the motor in reverse phase, and the motor reverses. When the reversing switch is again left open and no A. C. power passed into theA line the tube system immediately balances again, the relay de-energizes, and the motor stops. Inasmuch as the running contactor 8 is energized by the closing of either the forward or backward contactor of the tuning motor, the motor will always run, irrespective of whether a forward or backward connection is used. Thus the operator is able to listen to the signals, and with one hand manipulate reversing switch to change the tuning of the receiver slightly, as he desires. When using heterodyne equipment, the operator will be able to tell by the tone heard in his receiver whether he is approaching the signal or receding from it, since the pitch of the beat note heard will vary in accord with the relation of the signal frequency to the local oscillator frequency. If the directionof tuning is incorrect, the operator may reverse it by throwing the switch 50 to the other side. To maintain the proper phasal relations at the double anode tubes, it is obvious that suitable phase shifting equipment may be used, such phase shifting means being well known in the art. g

The amount of A. C. power passed through the telephone pair need only be small because of the amplification of the tube system utilized at the receiving station, and as it is straight alternating current no interference with standard telephone equipment is encountered, and both signals and tuning power can thus be passed over telephone pairs where only audio frequency rights are available.

With some telephone lines the repeating equipment available does not have a low frequency range adequate to care for the transmission of -cycle signals; with others, there may be interference between the ringing currents and the tuning equipment.' In such cases it is obvious that we may use frequencies higher than 60 cycles, which would, however, be tied together as between the transcribing station and the receiving station through the medium of the common alternating power system as described. For this purpose, it is obvious that frequency multipliers may be used at both ends of the two-wire line, involving synchronous motors and generators, saturated-core transformers which generate harmonics of the power supply frequency, the use of a series of passive full-wave rectiers serving as frequency doublers, or any other Similar equipment for the multiplication of frequencies, such as are well known to the art.

It will also be apparent that the tuning motor need. not be driven, as we have shown from the common A. C. power system. The motor arrangement shown is desirable, but we deem as full equivalents thereof the use of a separate power system, which need not be in synchronism with the common system, or a direct current motor, or the use of mechanical reversing means actuable by the polar relay system shown.

We claim:

l. Apparatus for remote control comprising a two-wire line to apparatus to be controlled, comprising four cathode-anode current paths in each of which is disposed a control electrode, means for so energizing said anodes from an alternating current supply system that two of said anodes shall be in phase opposition to the remaining two of said anodes, means for passing current from said A. C. supply system over said two-wire line, means for impressing said A. C. supply system current upon two of said control electrodes in similar phase relationship, and upon the remaining two of said control electrodes in phase opposition thereto.

2. Apparatus for remote control comprising a two-wire line to apparatus to be controlled, two full-wave grid-controlled rectifying units, having four cathode-anode current paths, with a grid disposed in each of said paths, having two anodes of said rectifying units energized in parallel from a commercial alternating current power source, and the remaining two anodes thereof energized in parallel from said source in phase opposition to said first mentioned anodes; means for directing current from said commercial A. C. power source onto said two-wire line at a control station, means associated with said rectier units for applying current from said control station over said two-wire line to two of said grids in phase similarity, and to the remaining two grids in phase opposition thereto, and means for changing the phasal relation of the current applied to said grids relative to that on said anodes; a motor actuated by said A. C. power source, and means for controlling the direction of actuation of said motor responsive to the output of said rectiier unit.

3. Apparatus for remote control, including a two-wire line over which audio-frequency rights only are available, which comprises a motor operable by direct current in direction responsive to the direction of flow of said current, means for producing a pulsating direct current from a commercial A. C. source, means for controlling the direction of said current in accord with the phase relations between said A. C. supply and an alternating current received over said two-wire lines, and means at a control station for directing an alternating current over said line and changing the phase relation thereof to said A. C. supply.

4. Apparatus for remote control from a station connected to controllable apparatus by a twowire line over which audio-frequency rights only are available, comprising means for impressing current uponY said line at said station from a commercial ALC. power supply system, means at said receiving station energized lfrom said commercial A. C. power supply system for producing a pulsating direct current at said apparatus to be controlled, means actuated by current received over said two-wire line for controlling the direction of flow of said pulsating direct current, and means responsive to the direction of flow of said pulsating direct current for directly controlling said apparatus.

5. Apparatus for remote control from a control station connected by a two-wire line over which audio-frequency rights only are available to rotationally controllable apparatus, comprising means for impressing current from an A. C. power supply system upon said two-wire line at said control station, means energized from said A. C. power supply for producing a pulsating direct current at said controllable apparatus, means for controlling the direction of Ilow of said direct current in accord with the phasal relations between the current from said A, C. power supply applied to said D. C. producing means and that received from said two-wire line, and directly controlling means energized by said pulsating direct current and responsive to the direction of said current ilow.

6. A device for remote control of rotationally controllable apparatus from a station connected by a two-wire line over which audio-frequency rights only are available to said apparatus which comprises a reversible tuning motor, a diierential polar relay through operation of which the direction of rotation of said motor may be changed,

two full-wave rectifier units having anodes, grids, and cathodes, two of said anodes being energized in phase, and two in phase opposition from a commercial A. C. power supply, means for connecting said differential relay to said rectier units whereby the direction of actuation o1' said relay is dependent; upon the grid energization of said rectifier unit, and means for directing a current from said A. C. source at said control station to said rectiiier unit and for controlling the phase relation of said current to said anode energization.

7. Means for remotely controlling the rotational position of apparatus connected to a control station by two wires on which only audio-frequency rights are available, comprising a reversible motor, a polar relay arranged to control the direction of rotation of said motor, two full-Wave rectifier units having anodes, cathodes, and control grids disposed within an evacuated envelope. two of said anodes being energized in phase and two in phase opposition from a commercial A. C. power supply, said relay being so connected and arranged with said rectifier units that the direction of relay actuation is dependent upon the grid energization of said units, means for directing a current from said A. C. source at said control station to said rectier unit, and means for controlling the phase relation of said current to said anode energization.

- CHESTER PELMULDER.

HANS O. STORM. 

